Viscoelastic surfactant fluids and related methods of use

ABSTRACT

Viscoelastic surfactant based aqueous fluid systems useful as thickening agents in various applications, e.g. to suspend particles produced during the excavation of geologic formations. The surfactants are zwitterionic/amphoteric surfactants such as dihydroxyl alkyl glycinate, alkyl ampho acetate or propionate, alkyl betaine, alkyl amidopropyl betaine and alkylimino mono- or di-propionates derived from certain waxes, fats and oils. The thickening agent is used in conjunction with an inorganic water-soluble salt or organic additive such as phthalic acid, salicylic acid or their salts.

FIELD OF THE INVENTION

[0001] This application is a continuation application of U.S. Ser. No.09/093,131, filed Jun. 8, 1998, which claims the benefit of thedisclosure of U.S. Provisional Patent Application Serial No. 60/049,045,filed on Jun. 10, 1997, and 60/054,455, filed on Aug. 5, 1997. Thedisclosure of U.S. Serial No. 09/093,131, filed Jun. 8, 1998, isincorporated herein it its entirety.

[0002] This invention relates to viscoelastic fluids which contain asurfactant and to methods of suspending particles using suchviscoelastic fluids.

BACKGROUND OF THE INVENTION

[0003] It is known to thicken the aqueous phase of a suspension of solidparticles or emulsified droplets. The addition of thickeners increasesthe viscosity of the aqueous phase and thereby retards settling of theparticles or droplets. Such retardation is useful to maintain theparticles or droplets in suspension during the storage, use, and/ortransport of the suspension.

[0004] Polymeric thickeners, e.g. starches, which thicken byentanglement of the polymeric chains, have been used to viscosify theaqueous phase of suspensions. Such thickeners can degrade under theinfluence of mechanical shear or chemical scission (e.g. by oxidation orhydrolysis) of the polymeric chains which results in a loss of viscosityand, thus, suspension stability.

[0005] Cationic surfactants have been found which form rod-Like micellesunder certain conditions. The presence of the rod-Like micelles impartsto the fluid viscoelastic properties. However, cationic surfactants tendto have high toxicity and very low biodegradability.

SUMMARY OF THE INVENTION

[0006] The present invention provides a viscoelastic fluid useful as athickener for the suspension of particles. The viscoelastic fluidsconsist of an amphoteric/zwitterionic surfactant and an organicacid/salt and/or inorganic salts.

[0007] Thus, this invention specifically relates to a viscoelastic fluidcomprising:

[0008] (1) an aqueous medium;

[0009] (2) an amount of a surfactant selected from the group consistingof amphoteric surfactants, zwitterionic surfactants, and mixturesthereof, effective to render said aqueous medium viscoelastic; and

[0010] (3) a member selected from the group consisting of organic acids,organic acid salts, inorganic salts, and combinations of one or moreorganic acids or organic acid salts with one or more inorganic salts.

[0011] In yet another embodiment of the present invention, the inventionrelates to a viscoelastic fluid consisting essentially of:

[0012] (1) an aqueous medium;

[0013] (2) an amount of a surfactant comprising an amine oxidesurfactant; and

[0014] (3) an anionic surfactant containing a hydrophobe having at least14 carbon atoms.

[0015] The term “viscoelastic” refers to those viscous fluids havingelastic properties, i.e., the liquid at least partially returns to itsoriginal form when an applied stress is released. The thickened aqueousviscoelastic fluids are useful as water-based hydraulic fluids inlubricant and hydraulic fracturing fluids to increase permeability inoil production.

[0016] The present invention also relates to a method for distributingsuspended solid particles such as excavation by-products in a fluidcomprised of the viscoelastic fluid of this invention, wherein the solidparticles remain suspended for an extended period of time to a side, bytransporting the fluid to a site while the solid particles remainsuspended in the fluid and depositing the fluid to such site.

[0017] This invention also relates to a method for fracturing asubterranean formation comprising pumping the inventive viscoelasticfluid through a wellbore and into a subterranean formation at a pressuresufficient to fracture the formation.

[0018] This invention also relates to a detergent formulation comprisinga detersive surfactant in admixture with a viscoelastic fluid of thisinvention.

[0019] This invention also relates to the use of the viscoelastic fluidas a drift control agent for agricultural formulations. In this regard,this invention relates to an aqueous formulation of an agriculturalchemical and an amount of the viscoelastic fluid of this inventionsufficient to increase the average droplet size of a spray of saidformulation.

BRIEF DESCRIPTION OF THE FIGURES

[0020]FIG. 1 shows viscosity versus shear rate for a viscoelasticsurfactant solution prepared by adding 5 percent of disodiumtallowiminodipropionate (Mirataine T2C®) and 2.25 percent of phthalicacid to water.

[0021]FIG. 2 shows the dynamic modulus G′(storage modulus) and G″ (lossmodulus) at 25° C. and 50° C. of the same solution as FIG. 1.

[0022]FIG. 3 shows the viscosity versus shear rate for a viscoelasticsurfactant solution prepared by adding 5 percent of disodiumtallowiminodipropionate (Mirataine T2C®), 4 percent of NH₄Cl and1.75˜2.0 percent of phthalic acid to water.

[0023]FIG. 4 shows the viscosity versus shear rate for viscoelasticsurfactant solutions prepared by adding 4 or 5 percent of disodiumoleamidopropyl betaine (Mirataine BET-O®), 3 percent of KCl and 0.5percent of phthalic acid to water.

[0024]FIG. 5 shows the dynamic modulus G′(storage modulus) and G″ (lossmodulus) at 25° C. and 50° C. of the same solution as FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

[0025] The property of viscoelasticity in general is well known andreference is made to S. Gravsholt, Journal of Coll. And Interface Sci.,57(3), 575 (1976); Hoffmann et al., “Influence of Ionic Surfactants onthe Viscoelastic Properties of Zwitterionic Surfactant Solutions”,Langmuir, 8, 2140-2146 (1992); and Hoffmann et al., The RheologicalBehaviour of Different Viscoelastic Surfactant Solutions, Tenside Surf.Det., 31, 389-400, 1994. Of the test methods specified by thesereferences to determine whether a liquid possesses viscoelasticproperties, one test which has been found to be useful in determiningthe viscoelasticity of an aqueous solution consists of swirling thesolution and visually observing whether the bubbles created by theswirling recoil after the swirling is stopped. Any recoil of the bubblesindicates viscoelasticity. Another useful test is to measure the storagemodulus (G′) and the loss modulus (G″) at a given temperature. If G′>G″at some point or over some range of points below about 10 rad/sec,typically between about 0.001 to about 10 rad/sec, more typicallybetween about 0.1 and about 10 rad/sec, at a given temperature and ifG′>10⁻² Pascals, preferably 10⁻¹ Pascals, the fluid is typicallyconsidered viscoelastic at that temperature. Rheological measurementssuch as G′ and G″ are discussed more fully in “RheologicalMeasurements”, Encyclopedia of Chemical Technology, vol. 21, pp.347-372, (John Wiley & Sons, Inc., N.Y., N.Y., 1997, 4th ed.). To theextent necessary for completion, the above disclosures are expresslyincorporated herein by reference.

[0026] Viscoelasticity is caused by a different type of micelleformation than the usual spherical micelles formed by most surfactants.Viscoelastic surfactant fluids form worm-like, rod-like or cylindricalmicelles in solution. The formation of long, cylindrical micellescreates useful rheological properties. The viscoelastic surfactantsolution exhibits shear thinning behavior, and remains stable despiterepeated high shear applications. By comparison, the typical polymericthickener will irreversibly degrade when subjected to high shear.

[0027] In the summary of the invention and this detailed description,each numerical value should be read once as modified by the term“about”(unless already expressly so modified), and then read again asnot so modified, unless otherwise indicated in context.

[0028] The viscoelastic surfactants can be either ionic or nonionic. Thepresent invention comprises an aqueous viscoelastic surfactant based onamphoteric or zwitterionic surfactants. The amphoteric surfactant is aclass of surfactant that has both a positively charged moiety and anegatively charged moiety over a certain pH range (e.g. typicallyslightly acidic), only a negatively charged moiety over a certain pHrange (e.g. typically slightly alkaline) and only a positively chargedmoiety at a different pH range (e.g. typically moderately acidic), whilea zwitterionic surfactant has a permanently positively charged moiety inthe molecule regardless of pH and a negatively charged moiety atalkaline pH.

[0029] The viscoelastic fluid comprises water, surfactant, and awater-soluble compound selected from the group consisting of organicacids, organic acid salts, inorganic salts, and mixtures thereof.Alternatively, the viscoelastic fluid can comprise water, an amine oxidesurfactant and an anionic surfactant containing a hydrophobe having atleast about 14 carbon atoms. The viscoelastic surfactant solution isuseful as a fracturing fluid or water-based hydraulic fluid. Theviscoelastic fluid used as a fracturing fluid may optionally contain agas such as air, nitrogen or carbon dioxide to provide an energizedfluid or a foam.

[0030] The component of the fluid which will be present in the greatestconcentration is water, i.e. typically water will be a major amount byweight of the viscoelastic fluid. Water is typically present in anamount by weight greater than or equal to about 50% by weight of thefluid. The water can be from any source so long as the source containsno contaminants which are incompatible with the other components of theviscoelastic fluid (e.g., by causing undesirable precipitation). Thus,the water need not be potable and may be brackish or contain othermaterials typical of sources of water found in or near oil fields.

[0031] Examples of zwitterionic surfactants useful in the presentinvention are represented by the formula:

[0032] wherein R₁ represents a hydrophobic moiety of alkyl,alkylarylalkyl, alkoxyalkyl, alkylaminoalkyl and alkylamidoalkyl,wherein alkyl represents a group that contains from about 12 to about 24carbon atoms which may be branched or straight chained and which may besaturated or unsaturated. Representative long chain alkyl groups includetetradecyl (myristyl), hexadecyl (cetyl), octadecentyl (oleyl),octadecyl (stearyl), docosenoic (erucyl) and the derivatives of tallow,coco, soya and rapeseed oils. The preferred alkyl and alkenyl groups arealkyl and alkenyl groups having from about 16 to about 22 carbon atoms.Representative of alkylamidoalkyl is alkylamidopropyl with alkyl beingas described above.

[0033] R₂ and R₃ are independently an aliphatic chain (i.e. as opposedto aromatic at the atom bonded to the quaternary nitrogen, e.g., alkyl,alkenyl, arylalkyl, hydroxyalkyl, carboxyalkyl, andhydroxyalkyl-polyoxyalkylene, e.g. hydroxyethyl-polyoxyethylene orhydroxypropyl-polyoxypropylene) having from 1 to about 30 atoms,preferably from about 1 to about 20 atoms, more preferably from about 1to about 10 atoms and most preferably from about 1 to about 6 atoms inwhich the aliphatic group can be branched or straight chained, saturatedor unsaturated. Preferred alkyl chains are methyl, ethyl, preferredarylalkyl is benzyl, and preferred hydroxyalkyls are hydroxyethyl orhydroxypropyl, while preferred carboxyalkyls are acetate and propionate.

[0034] R₄ is a hydrocarbyl radical (e.g. alkylene) with chain length 1to 4. Preferred are methylene or ethylene groups.

[0035] Specific examples of zwitterionic surfactants include thefollowing structures:

[0036] wherein R₁ has been previously defined herein.

[0037] Examples of amphoteric surfactants include those represented byformula VI:

[0038] wherein R₁, R₂, and R₄ are the same as defined above.

[0039] Other specific examples of amphoteric surfactants include thefollowing structures:

[0040] wherein R₁ has been previously defined herein, and X is aninorganic cation such as Na⁺, K⁺, NH₄ ⁺ associated with a carboxylategroup or hydrogen atom in an acidic medium.

[0041] A typical chemical process to synthesize dihydroxy ethoxylateglycinate starting from ethoxylated alkylamine is as follows:

[0042] The final products may also include some unreacted startingdihydroxy ethyl alkyl amine, and small amounts of sodium glycolate,diglycolate and sodium chloride as by products. A similar process can beused to prepare propoxylated analogues.

[0043] A typical chemical process to synthesize alkyliminiodipropionatefrom alkyl amine is as follows:

[0044] The final products will also include a small amount of methanol,unreacted acrylic acid, alkylamine and some oligomeric acrylate or acidas by products.

[0045] A typical chemical process to synthesize alkylamidopropyl betainefrom alkyl amine is as follows:

[0046] The final products will also include a small amount of sodiumglycolate, diglycolate, sodium chloride and glycerine as by products.

[0047] In still another embodiment of the invention, the zwitterionicsurfactant selected is an amine oxide. This material has the followingstructure:

[0048] where R₁, R₂ and R₃ are as defined above.

[0049] The surfactants are used in an amount which in combination withthe other ingredients is sufficient to form a viscoelastic fluid, whichamount will typically be a minor amount by weight of the fluid (e.g.less than about 50% by weight). The concentration of surfactant canrange from about 0.5% to about 10% percent by weight of the fluid, moretypically from about 0.5% to about 8%, and even more typically fromabout 0.5% to about 6%. Optimum concentrations for any particular set ofparameters can be determined experimentally.

[0050] The fluid also comprises one or more members from the group oforganic acids, organic acid salts, and inorganic salts. Mixtures of theabove members are specifically contemplated as falling within the scopeof the invention. This member will typically be present in only a minoramount (e.g. less than about 20% by weight of the fluid).

[0051] The organic acid is typically a sulfonic acid or a carboxylicacid and the anionic counter-ion of the organic acid salts are typicallysulfonates or carboxylates. Representative of such organic moleculesinclude various aromatic sulfonates and carboxylates such as p-toluenesulfonate, naphthalene sulfonate, chlorobenzoic acid, salicylic acid,phthalic acid and the like, where such counter-ions are water-soluble.Most preferred are salicylate, phthalate, p-toluene sulfonate,hydroxynaphthalene carboxylates, e.g. 5-hydroxy-1-naphthoic acid,6-hydroxy-1-naphthoic acid, 7-hydroxy-1-naphthoic acid,1-hydroxy-2-naphthoic acid, preferably 3-hydroxy-2-naphthoic acid,5-hydroxy-2-naphthoic acid, 7-hydroxy-2-naphthoic acid, and1,3-dihydroxy-2-naphthoic acid and 3,4-dichlorobenzoate. The organicacid or salt thereof typically aids the development of increasedviscosity which is characteristic of preferred fluids. Without wishingto be bound by any theory unless expressly noted otherwise in context,it is thought that association of the organic acid or salt thereof withthe micelle decreases the aggregation curvature of the micelle and thuspromotes the formation of a worm-like or rod-like micelle. The organicacid or salt thereof will typically be present in the viscoelastic fluidat a weight concentration of from about 0.1% to about 10%, moretypically from about 0.1% to about 7%, and even more typically fromabout 0.1% to about 6%.

[0052] The inorganic salts that are particularly suitable for use in theviscoelastic fluid include water-soluble potassium, sodium, and ammoniumsalts, such as potassium chloride and ammonium chloride. Additionally,calcium chloride, calcium bromide and zinc halide salts may also beused. The inorganic salts may aid in the development of increasedviscosity which is characteristic of preferred fluids. Further, theinorganic salt may assist in maintaining the stability of a geologicformation to which the fluid is exposed. Formation stability and inparticular clay stability (by inhibiting hydration of the clay) isachieved at a concentration level of a few percent by weight and as suchthe density of fluid is not significantly altered by the presence of theinorganic salt unless fluid density becomes an important consideration,at which point, heavier inorganic salts may be used. The inorganic saltwill typically be present in the viscoelastic fluid at a weightconcentration of from about 0.1% to about 30%, more typically from about0.1% to about 10%, and even more typically from about 0.1% to about 8%.Organic salts, e.g. trimethylammonium hydrochloride andtetramethylammonium chloride, may also be useful in addition to, or as areplacement for, the inorganic salts.

[0053] As an alternative to the organic salts and inorganic salts, or asa partial substitute therefor, one can use a medium to long chainalcohol (preferably an alkanol), preferably having five to ten carbonatoms, or an alcohol ethoxylate (preferably an alkanol ethoxylate)preferably of a 12 to 16 carbon alcohol and having 1 to 6, preferably1-4, oxyethylene units.

[0054] In the embodiment where the surfactant selected is an amineoxide, it is preferably used in combination with an anionic surfactantcontaining a hydrophobe having at least about 14 carbon atoms. Examplesof suitable anionic surfactants include alkyl sulfates or sulfonateshaving alkali metal counter ions or alkyl carboxylates, wherein alkylrepresents a group that contains from about 14 to about 24 carbon atomswhich may be branched or straight chained and which may be saturated orunsaturated, and more preferably contains between about 16 and about 22carbon atoms.

[0055] For this embodiment (amine oxide/anionic surfactant) the weightratio of the amine oxide to anionic surfactant is from about 100:1 toabout 50:50.

[0056] In addition to the water-soluble salts and thickening agentsdescribed hereinbefore, the viscoelastic fluid used as a hydraulicfracturing fluid may contain other conventional constituents whichperform specific desired functions, e.g., corrosion inhibitors,fluid-loss additives and the like. A proppant can be suspended in thefracturing fluid. The pH of the fluid will typically range from stronglyacidic (e.g. Less than a pH of about 3) to slightly alkaline (e.g. froma pH just greater than 7.0 to about 8.5, more typically to about 8.0) ormoderately alkaline (e.g. a pH of about 8.5 to about 9.5). Stronglyalkaline pHs (e.g. above a pH of about 10) should be avoided.

[0057] It is also conceivable to combine the aboveamphoteric/zwitterionic surfactants with conventional anionic, nonionicand cationic surfactants to get the desired viscoelastic fluid for askilled worker. In typical embodiments, the amphoteric/zwitterionicsurfactant is typically present in a major amount by weight of allsurfactants, and more typically is essentially the only surfactantpresent. Typically, the viscoelastic fluid will be essentially free ofanionic surfactants, e.g. it will contain less than about 0.5%, moretypically less than about 0.2%, even more typically less than 0.1% byweight of anionic surfactants.

[0058] To prepare the aqueous fluids in accordance with the presentinvention, the surfactant is added to an aqueous solution in which hasbeen dissolved a water-soluble inorganic salt, e.g. potassium chlorideor ammonium chloride and/or at least one organic acid or water-solubleorganic acid salt to provide selective control of the loss of particlesuspension properties. In the embodiment wherein the fluid is a mixtureof water, and amine oxide surfactant and an anionic surfactant, a simplemixture of the three components is utilized. Standard mixing proceduresknown in the art can be employed since heating of the solution andspecial agitation conditions are normally not necessary. Of course, ifused under conditions of extreme cold such as found in Alaska, normalheating procedures should be employed. It has been found in someinstances preferable to dissolve the thickener into a lower molecularweight alcohol prior to mixing it with the aqueous solution. The lowermolecular weight alcohol, for instance isopropanol, functions as an aidto solubilize the thickener. Other similar agents may also be employed.Further, a defoaming agent such as a polyglycol may be employed toprevent undesirable foaming during the preparation of the viscoelasticfluid if a foam is not desirable under the conditions of the treatment.If a foam or gas-energized fluid is desired, any gas such as air,nitrogen, carbon dioxide and the like may be added.

[0059] The fluid of this invention is particularly useful in thehandling of particles generated during the excavation of a geologicformation, e.g. digging, drilling, blasting, dredging, tunneling, andthe like, for example in the course of constructing roads, bridges,buildings, mines, tunnels and the like. The particles are mixed with theviscoelastic fluid by means which are effective to disperse theparticles in the fluid. The particles generally have a particle sizeranging from a fine powder to coarse gravel, e.g. dust, sand, andgravel. Particle size affects the suspendability of excavationprocessing wastes. For example, small particles suspend better thanlarge particles, and very fine particles suspend so well that themixture may become too thick to transport by pump or similar means. Thedistribution of excavation processing waste sizes is also important, aswaste which contains particles which span a wide range of sizes is moreeasily suspended than waste wherein the particles are of about the samesize. Therefore, it may be preferred to screen the waste particles priorto applying the present method to scalp off the particles that are toolarge to suspend to obtain a better particle size distribution.

[0060] The viscoelastic fluids of the present invention can be utilizedto carry earth or materials excavated during boring, excavating andtrenching operations in the deep foundation construction industry, thesubterranean construction industry and in tunneling, in well drillingand in other applications of earth support fluids. The ability of theexcavation tools or systems to hold and remove increased loading ofearth is improved by the suspending properties and lubricatingproperties of the surfactant viscoelastic fluids.

[0061] In one preferred embodiment of this invention, the surfactant canbe combined with some fluid-loss control additives known in the industrylike water-soluble or water-dispersible polymers (guar and guarderivatives, xanthan, polyacrylamide, starch and starch derivatives,cellulosic derivatives, polyacrylates, polyDADMAC [poly(diallyl dimethylammonium chloride] and combinations thereof), clay (Bentonite andattapulgite) in order to give fluid-loss control properties to theexcavating fluid and contribute to the stabilization of the wall of theexcavation.

[0062] More comprehensive information can be found in The University ofHouston, Department of Chemical Engineering, Publication No UHCE 93-1entitled, Effect of Mineral and Polymer slurries on Perimeter LoadTransfer in Drilled shafts, published in January 1993, and PCT WO96/23849, the disclosures of which are incorporated by reference.

[0063] The above method for suspending solids has many applications,particularly in mining and the handling of mine tailings. The disclosureof U.S. Pat. No. 5,439,317 (Bishop et al.) is incorporated by referencein this regard. One application is to transport and place mineralprocessing waste in underground caverns or below grade cavities. Anotherapplication is for backfilling of open pits or quarries without the useof costly and labor intensive equipment for deployment. Additionally,the method can be used to place clay or other liners in holding orstorage ponds that are used to hold liquids and to prevent the entry ofthese liquids into the ground water regime and/or to place liners inlandfills for a similar purpose. Another application of the method, isfor the extinguishing and/or containment of coal mine fires by deployingquantities of solids below ground to seal the fire from sources ofoxygen. Still another application of the method is to place solids inpreviously mined cavities to prevent surface subsidence.

[0064] The hydraulic fracturing method of this invention uses otherwiseconventional techniques. The disclosure of U.S. Pat. No. 5,551,516(Norman et al.) is incorporated by reference in this regard. Oil-fieldapplications of various materials are described in “Oil-fieldApplications”, Encyclopedia of Polymer Science and Engineering, vol. 10,pp. 328-366 (John Wiley & Sons, Inc., New York, N.Y., 1987) andreferences cited therein, the disclosures of which are incorporatedherein by reference thereto.

[0065] Hydraulic fracturing is a term that has been applied to a varietyof methods used to stimulate the production of fluids such as oil,natural gas etc., from subterranean formations. In hydraulic fracturing,a fracturing fluid is injected through a wellbore and against the faceof the formation at a pressure and flow rate at least sufficient toovercome the overburden pressure and to initiate and/or extend afracture(s) into the formation. The fracturing fluid usually carries aproppant such as 20-40 mesh sand, bauxite, glass beads, etc., suspendedin the fracturing fluid and transported into a fracture. The proppantthen keeps the formation from closing back down upon itself when thepressure is released. The proppant filled fractures provide permeablechannels through which the formation fluids can flow to the wellbore andthereafter be withdrawn. Viscoelastic fluids have also been extensivelyused in gravel pack treatment.

[0066] In addition to the applications discussed above, the viscoelasticfluids may also be used as an industrial drift control agent, or as arheology modifier for personal care formulations (e.g. cleansers,conditioners, etc.) and household cleansers (e.g. detergentformulations). A detergent formulation of the viscoelastic fluids ofthis invention will further comprise a detersive surfactant. Examples ofdetersive surfactants and other conventional ingredients of detergentand/or personal care formulations are disclosed in U.S. Ser. No.08/726,437, filed Oct. 4, 1996, the disclosure of which is incorporatedherein by reference.

[0067] Typically, the detersive surfactant will be anionic or nonionic.Preferred water-soluble anionic organic surfactants herein includelinear alkyl benzene sulfonates containing from about 10 to about 18carbon atoms in the alkyl group; branched alkyl benzene sulfonatescontaining from about 10 to about 18 carbon atoms in the alkyl group;the tallow range alkyl sulfates; the coconut range alkyl glycerylsulfonates; alkyl ether (ethoxylated) sulfates wherein the alkyl moietycontains from about 12 to 18 carbon atoms and wherein the average degreeof ethoxylation varies between 1 and 12, especially 3 to 9; the sulfatedcondensation products of tallow alcohol with from about 3 to 12,especially 6 to 9, moles of ethylene oxide; and olefin sulfonatescontaining from about 14 to 16 carbon atoms.

[0068] Specific preferred anionics for use herein include: the linearC₁₀-C₁₄ alkyl benzene sulfonates (LAS); the branched C₁₀-C₁₄ alkylbenzene sulfonates (ABS); the tallow alkyl sulfates, the coconut alkylglyceryl ether sulfonates; the sulfated condensation products of mixedC₁₀-C₁₈ tallow alcohols with from about 1 to about 14 moles of ethyleneoxide; and the mixtures of higher fatty acids containing from 10 to 18carbon atoms.

[0069] Particularly preferred nonionic surfactants for use in liquid,powder, and gel applications include the condensation product of C₁₀alcohol with 3 moles of ethylene oxide; the condensation product oftallow alcohol with 9 moles of ethylene oxide; the condensation productof coconut alcohol with 5 moles of ethylene oxide; the condensationproduct of coconut alcohol with 6 moles of ethylene oxide; thecondensation product of C₁₂ alcohol with 5 moles of ethylene oxide; thecondensation product of C₁₂₋₁₃ alcohol with 6.5 moles of ethylene oxide,and the same condensation product which is stripped so as to removesubstantially all lower ethoxylate and non-ethoxylated fractions; thecondensation product of C₁₂-C₁₃ alcohol with 2.3 moles of ethyleneoxide, and the same condensation product which is stripped so as toremove substantially all lower ethoxylated and non-ethoxylatedfractions; the condensation product of C₁₂-C₁₃ alcohol with 9 moles ofethylene oxide; the condensation product of C₁₄-C₁₅ alcohol with 2.25moles of ethylene oxide; the condensation product of C₁₄-₁₅ alcohol with4 moles of ethylene oxide; the condensation product of C₁₄-₁₅ alcoholwith 7 moles of ethylene oxide; and the condensation product of C₁₄-₁₅alcohol with 9 moles of ethylene oxide.

[0070] Particular detersive applications for which the viscoelasticfluid will be useful include as a thickener for acidic bathroomcleaners, such as those disclosed in U.S. Pat. No. 5,639,722 (Kong etal.) and shower gels such as those disclosed in U.S. Pat. No. 5,607,678(Moore et al.), the disclosures of which are incorporated by reference.The viscoelastic fluids will also be useful in the manufacture ofbuilding products based on plaster, plaster/lime, lime/cement or cementsuch as those disclosed in U.S. Pat. No. 5,470,383 (Schermann et al.)and foam fluids such as those disclosed in U.S. Pat. No. 5,258,137(Bonekamp et al.), the disclosures of which are incorporated byreference. In particular, the fluid will be useful for improving thewater retention of cement slurries and grouts allowing betterpumpability and workability with minimal free water. The fluids willalso be useful as thickeners for acidic (e.g. a pH of less than about 5)aqueous slurries of mineral carbonates or oxides, e.g. iron oxide,cerium oxide, silica suspensions, titanium oxide, calcium carbonate, andzirconium oxide. In this regard, the disclosure of U.S. Pat. No.4,741,781 (De Witte) is incorporated by reference.

[0071] The viscoelastic fluid of this invention will also be useful informulations for the agricultural delivery of solid fertilizers andpesticides such as micronutrients, biologicals, insecticides,herbicides, fungicides, and plant growth regulators. Such formulationsare typically aqueous suspensions or solutions comprised of a majoramount of water and an agriculturally effective amount of anagriculturally useful chemical. The viscoelastic fluid is typicallycombined with the other ingredients of the formulation in an amount thateffectively reduces the number of droplets below about 150 microns, i.e.the droplets most responsible for drift problems.

[0072] The following examples are presented to illustrate thepreparation and properties of aqueous viscoelastic surfactant basedhydraulic fluids and should not be construed to limit the scope of theinvention, unless otherwise expressly indicated in the appended claims.All percentages, concentrations, ratios, parts, etc. are by weightunless otherwise noted or apparent from the context of their use.

EXAMPLES Example 1

[0073] Viscoelastic surfactant solutions are prepared by adding 5percent of ammonium chloride and 3 to 5 percent of dihydroxyethyl tallowglycinate (Mirataine TM®) to water. The systems were stirred until allof the surfactant dissolved. All of the samples were observed to beviscoelastic by the bubble recoil test. Rheology of solution wasmeasured by Rheometric ARES at 25° C. The results are given below inTable 1. TABLE 1 Shear rate Viscosity (cps) in 5% NH₄Cl (sec⁻¹) 3%Surfactant 4% Surfactant 5% Surfactant 10 1692.4 2619.8 3774.7 18 967.71490.6 2144 32 555.5 851.6 1214.3 56 319.2 483.2 688.1 100 184.6 278393.6 178 107.5 159.3 225.4

Example 2

[0074] In a manner similar to Example 1, 0.3 percent of phthalic acidand 2 to 4 percent of dihydroxyethyl tallow glycinate (Mirataine TM®)were put into solution. All of the samples were observed to beviscoelastic by the bubble recoil test. Rheological measurements wereperformed in the manner described in Example 1 at 25° C.

[0075] The results are shown below in Table 2: TABLE 2 Shear rateViscosity (cps) in 0.3% phthalic acid (sec⁻¹) 2% Surfactant 3%Surfactant 4% Surfactant 10 791.5 1474.6 1968.7 18 455.3 840.9 1101.5 32262.4 490 564.5 56 152 279.2 361.7 100 88 160.9 356.6 178 53 91.6 342.3

Example 3

[0076] The rheological measurements were also performed at highertemperatures by FANN Rheometer. The results for 4 percent dihydroxyethyltallow glycinate (Mirataine TM®) and 0.3 percent of phthalic acidsolution are shown below in Table 3: TABLE 3 Temperature (° F.)Viscosity at 100 rpm (cps) 82 170 129 51 189 30 239 22 288 15

Example 4

[0077] The viscoelastic surfactant solutions are prepared by adding 5percent of disodium tallowiminodipropionate (Mirataine T2C®) and 2.25percent of phthalic acid to water. The systems were stirred and warmedup to 50° C. until all of the phthalic acid dissolved. All of thesamples were observed to be viscoelastic by the bubble recoil test.Rheology was measured for viscosity and dynamic modulus G′(storagemodulus) and G″ (loss modulus) by a Rheometric SR-200 at 25° C. and 50°C. The results are shown in FIGS. 1 and 2.

Example 5

[0078] In a manner similar to Example 4, 5 percent of disodiumtallowiminodipropiohate (Mirataine T2C®), 4 percent of NH₄Cl and1.75˜2.0 percent of phthalic acid in water were mixed together. All ofthe samples were observed to be viscoelastic by the bubble recoil test.Rheological measurements were performed in the manner described inExample 4 at 25° C. The results are shown in FIG. 3.

Example 6

[0079] The viscoelastic surfactant solutions are prepared by addition of4˜5% percent of oleamidopropyl betaine (Mirataine BET-O®), 3% KCl and0.5% phthalic acid to water. The system was stirred until all phthalicacid dissolved. Rheology was measured for steady viscosity and dynamicmodulus G′/G″ by Rheometric ARES at 25° C. The results are shown inFIGS. 4 and 5.

Example 7

[0080] A viscoelastic surfactant solution is prepared by mixing togetherin 95.65 parts of water 4 parts of euricic amido propylene dimethylamine oxide and 0.35 parts of sodium oleyl sulfate. The pH is adjustedto 8 by the addition of NaOH. Its temperature stability is determined bymeasuring its viscosity in cps (at shear rate of 100 sec ⁻¹). Theresults are shown in Table 4.

Example 8

[0081] A viscoelastic surfactant solution is prepared by mixing togetherin 95.50 parts of water 4.0 parts of euricic amido propylene dimethylamine oxide and 0.50 parts of sodium oleyl sulfate. Its temperaturestability is determined by measuring its viscosity in cps(at shear rateof 100 sec ⁻¹). The results are shown in Table 4. TABLE 4 ViscosityViscosity Temperature (° F.) Example 8 Example 7 100 282 247 120 302 293140 308 305 160 168 237 180 162 166 200 230 231 220 119 193 240 50 63250 36 36 260 30 27 270 16 10

Example 9

[0082] A viscoelastic surfactant-solution is prepared by mixing togetherin 96.1 parts of water 3.0 parts of euricic amidopropyl amine oxide and0.9 parts of sodium behenyl sulfate. The pH is adjusted to 9 by theaddition of NaOH. Its temperature stability is determined by measuringits viscosity in cps (at shear rate of 100 sec ⁻¹). The results areshown in Table 5.

Example 10

[0083] A viscoelastic surfactant solution is prepared by mixing togetherin 94.8 parts of water 4.0 parts of euricic amidopropyl amine oxide and1.2 parts of sodium behenyl sulfate. The pH is adjusted to 9 by theaddition of NaOH. Its temperature stability is determined by measuringits viscosity in cps (at shear rate of 100 sec ⁻¹). The results areshown in Table 5. TABLE 5 Viscosity Viscosity Temperature (° F.) Example9 Example 10 100 175 234 120 168 226 140 169 297 160 256 518 180 309 454200 276 173 220 140 214 240 154 284 260 94 351 270 52 215 280 31 90 29025 40 300 17 4

What is claimed is:
 1. A viscoelastic fluid comprising: (1) an aqueousmedium; (2) a zwitterionic surfactant; and (3) a member selected fromthe group consisting of organic acids, organic acid salts, inorganicsalts, and combinations of one or more organic acids or organic acidsalts with one or more inorganic salts; wherein the zwitterionicsurfactant constitutes 77% or more by weight of all surfactants presentin the fluid; wherein the fluid exhibits the property ofviscoelasticity.
 2. The fluid as claimed in claim 1 wherein the amountof the zwitterionic surfactant is present at about 0.5% to about 10% byweight of the fluid.
 3. The fluid as claimed in claim 1 wherein theamount of the zwitterionic surfactant is present at about 0.5% to about8% by weight of the fluid.
 4. The fluid as claimed in claim 1 whereinthe amount of the zwitterionic surfactant is present at about 0.5% toabout 6% by weight of the fluid.
 5. The fluid of claim 1 wherein thezwitterionic surfactant constitutes 89% or more by weight of allsurfactants present in the fluid.
 6. The fluid of claim 1 wherein thezwitterionic surfactant constitutes 92% or more by weight of allsurfactants present in the fluid.
 7. The fluid of claim 1 furthercomprising an anionic surfactant, the anionic surfactant being presentat 1.2% or less by weight of the fluid.
 8. The fluid of claim 7 whereinthe anionic surfactant is present at 0.9% or less by weight of thefluid.
 9. The fluid of claim 7 wherein the anionic surfactant is presentat about 0.5% or less by weight of the fluid.
 10. The fluid as claimedin claim 1 wherein the zwitterionic surfactant has a quaternary ammoniumhydrophilic moiety.
 11. The fluid as claimed in claim 1 wherein thesurfactant has a carboxylate hydrophilic moiety.
 12. The fluid asclaimed in claim 1 wherein the member is an inorganic salt and ispresent at about 0.1% to about 30% by weight.
 13. The fluid as claimedin claim 1 wherein the member is an organic acid or salt thereof and ispresent at about 0.1% to about 10% by weight.
 14. The fluid as in claim1 wherein the surfactant is represented by the formula (I):

wherein R₁ represents alkyl, alkenyl, alkylarylalkylene,alkenylarylalkylene, alkylaminoalkylene, alkenylaminoalkylene,alkylamidoalkylene, or alkenylamidoalkylene, wherein each of the alkylgroups have from about 14 to about 24 carbon atoms and may be branchedor straight chained and saturated or unsaturated, and wherein thealkylene groups have from about 1 to about 6 carbon atoms, R₂ and R₃ areindependently aliphatic chains having from about 1 to about 30 carbonatoms, and R₄ is a hydrocarbyl radical with a chain length of about 1 toabout
 4. 15. The fluid of claim 14 wherein R₁ is selected from the groupconsisting of tetradecyl, hexadecyl, octadecenyl, and octadecyl.
 16. Thefluid of claim 15 wherein R₁ is an alkyl group derived from tallow,coco, soya bean, or rapeseed oil.
 17. The fluid of claim 14 wherein thealkyl and alkenyl groups of R₁ are selected from alkyl groups andalkenyl groups respectively having from about 16 to about 22 carbonatoms.
 18. The fluid of claim 14 wherein R₂ and R₃ are independentlyalkyl, alkenyl, arylalkyl, hydroxyalkyl, carboxyalkyl, orhydroxyalkylpolyoxyalkylene, each having about 1 to about 10 carbonatoms.
 19. The fluid of claim 14 wherein R₂ and R₃ are independentlymethyl, ethyl, benzyl, hydroxyethyl, hydroxypropyl, carboxymethyl, orcarboxyethyl.
 20. The fluid of claim 14 wherein R₄ is methylene orethylene.
 21. The fluid of claim 14 wherein R₂ and R₃ are eachbeta-hydroxyethyl.
 22. The fluid of claim 21 wherein R₁ isRCONHCH₂CH₂CH₂— wherein R is an alkyl group having from about 14 toabout 24 carbon atoms which may be branched or straight chained andwhich may be saturated or unsaturated.
 23. The fluid of claim 14 whereinR₂ and R₃ are each methyl.
 24. The fluid of claim 23 wherein R₁ isRCONHCH₂CH₂CH₂— wherein R is an alkyl group having from about 14 toabout 24 carbon atoms which may be branched or straight chained andwhich may be saturated or unsaturated.
 25. The fluid of claim 14 whereinthe zwitterionic surfactant is selected from the group consisting ofdihydroxyethyl glycinates and alkylamidopropyl betaines.
 26. The fluidof claim 25 wherein the zwitterionic surfactant is oleamidopropylbetaine.
 27. The fluid of claim 14 wherein the zwitterionic surfactantis present at from about 0.5% to about 6% by weight in the fluid. 28.The fluid of claim 27 further comprising an anionic surfactant, theanionic surfactant being present at 1.2% or less by weight of the fluid.29. The fluid of claim 28 wherein the anionic surfactant is present at0.9% or less by weight of the fluid, the zwitterionic surfactant beingpresent at 89% or more by weight of the fluid.
 30. The fluid of claim 25wherein the zwitterionic surfactant is present at from about 0.5% toabout 6% by weight in the fluid, the fluid further comprising an anionicsurfactant, the anionic surfactant being present at 1.2% or less byweight of the fluid.
 31. A viscoelastic fluid comprising: (1) an aqueousmedium; (2) a zwitterionic surfactant; and (3) a member selected fromthe group consisting of organic acids, organic acid salts, inorganicsalts, and combinations of one or more organic acids or organic acidsalts with one or more inorganic salts; (4) an anionic surfactant,wherein the ratio of zwitterionic surfactant to anionic surfactant is 3⅓ to 1 or greater; wherein the fluid exhibits the property ofviscoelasticity.
 32. The fluid as claimed in claim 31 wherein the amountof the zwitterionic surfactant is from about 0.5% to about 10% by weightof the fluid.
 33. The fluid as claimed in claim 31 wherein the amount ofthe zwitterionic surfactant is from about 0.5% to about 8% by weight ofthe fluid.
 34. The fluid as claimed in claim 31 wherein the amount ofthe zwitterionic surfactant is from about 0.5% to about 6% by weight ofthe fluid.
 35. The fluid of claim 31 wherein the ratio of zwitterionicsurfactant to anionic surfactant is greater than 5 to
 1. 36. The fluidof claim 31 wherein the ratio of zwitterionic surfactant to anionicsurfactant is 8 to 1 or greater.
 37. The fluid of claim 31 wherein theratio of zwitterionic surfactant to anionic surfactant is 12 to 1 orgreater.
 38. The fluid as claimed in claim 31 wherein the zwitterionicsurfactant has a quaternary ammonium hydrophilic moiety.
 39. The fluidas claimed in claim 31 wherein the surfactant has a carboxylatehydrophilic moiety.
 40. The fluid as claimed in claim 31 wherein themember is an inorganic salt and is present in an amount of from about0.1% to about 30% by weight.
 41. The fluid as claimed in claim 31wherein the member is an organic acid or salt thereof and is present inan amount of from about 0.1% to about 10% by weight.
 42. The fluid as inclaim 31 wherein the surfactant is represented by the formula (I):

wherein R₁ represents alkyl, alkenyl, alkylarylalkylene,alkenylarylalkylene, alkylaminoalkylene, alkenylaminoalkylene,alkylamidoalkylene, or alkenylamidoalkylene, wherein each of the alkylgroups have from about 14 to about 24 carbon atoms and may be branchedor straight chained and saturated or unsaturated, and wherein thealkylene groups have from about 1 to about 6 carbon atoms, R₂ and R₃ areindependently aliphatic chains having from about 1 to about 30 carbonatoms, and R₄ is a hydrocarbyl radical with a chain length of about 1 toabout
 4. 43. The fluid of claim 42 wherein R₁ is selected from the groupconsisting of tetradecyl, hexadecyl, octadecenyl, and octadecyl.
 44. Thefluid of claim 42 wherein R₁ is an alkyl group derived from tallow,coco, soya bean, or rapeseed oil.
 45. The fluid of claim 42 wherein thealkyl and alkenyl groups of R₁ are selected from alkyl groups andalkenyl groups respectively having from about 16 to about 22 carbonatoms.
 46. The fluid of claim 42 wherein R₂ and R₃ are independentlyalkyl, alkenyl, arylalkyl, hydroxyalkyl, carboxyalkyl, orhydroxyalkylpolyoxyalkylene, each having about 1 to about 10 carbonatoms.
 47. The fluid of claim 42 wherein R₂ and R₃ are independentlymethyl, ethyl, benzyl, hydroxyethyl, hydroxypropyl, carboxymethyl, orcarboxyethyl.
 48. The fluid of claim 42 wherein R₄ is methylene orethylene
 49. The fluid of claim 42 wherein R₂ and R₃ are eachbeta-hydroxyethyl.
 50. The fluid of claim 49 wherein R₁ isRCONHCH₂CH₂CH₂— wherein R is an alkyl group having from about 14 toabout 24 carbon atoms which may be branched or straight chained andwhich may be saturated or unsaturated.
 51. The fluid of claim 42 whereinR₂ and R₃ are each methyl.
 52. The fluid of claim 51 wherein R₁ isRCONHCH₂CH₂CH₂— wherein R is an alkyl group having from about 14 toabout 24 carbon atoms which may be branched or straight chained andwhich may be saturated or unsaturated.
 53. The fluid of claim 42 whereinthe zwitterionic surfactant is selected from the group consisting ofdihydroxyethyl glycinates and alkylamidopropyl betaines.
 54. The fluidof claim 53 wherein the zwitterionic surfactant is oleamidopropylbetaine.
 55. The fluid of claim 42 wherein the zwitterionic surfactantis present at about 0.5% to about 6.0% by weight of the fluid.
 56. Thefluid of claim 55 wherein the ratio of zwitterionic surfactant toanionic surfactant is greater than 5 to
 1. 57. The fluid of claim 56wherein the anionic surfactant is present at 1.2% or less by weight ofthe fluid.
 58. The fluid of claim 57 wherein the anionic surfactant ispresent at 0.9% or less by weight of the fluid.
 59. The fluid of claim53 wherein the zwitterionic surfactant is present at about 0.5% to about6.0% by weight of the fluid.
 60. The fluid of claim 59 wherein the ratioof zwitterionic surfactant to anionic surfactant is greater than 5 to 1.61. The fluid of claim 60 wherein the anionic surfactant is present at1.2% or less by weight of the fluid.
 62. The fluid of claim 61 whereinthe anionic surfactant is present at 0.9% or less by weight of thefluid.
 63. A viscoelastic fluid comprising: (1) an aqueous medium; (2) azwitterionic surfactant; and (3) a member selected from the groupconsisting of organic acids, organic acid salts, inorganic salts, andcombinations of one or more organic acids or organic acid salts with oneor more inorganic salts; and (4) an anionic surfactant, wherein theanionic surfactant is present at 1.2% or less by weight of the fluid;wherein the fluid exhibits the property of viscoelasticity.
 64. Thefluid as claimed in claim 63 wherein the amount of the zwitterionicsurfactant is from about 0.5% to about 10% by weight of the fluid. 65.The fluid as claimed in claim 63 wherein the amount of the zwitterionicsurfactant is from about 0.5% to about 8% by weight of the fluid. 66.The fluid as claimed in claim 63 wherein the amount of the zwitterionicsurfactant is from about 0.5% to about 6% by weight of the fluid. 67.The fluid of claim 63 wherein the anionic surfactant is present at 0.9%or less by weight of the fluid.
 68. The fluid of claim 63 wherein theanionic surfactant is present at about 0.5% or less by weight of thefluid.
 69. The fluid as claimed in claim 63 wherein the zwitterionicsurfactant has a quaternary ammonium hydrophilic moiety.
 70. The fluidas claimed in claim 63 wherein the surfactant has a carboxylatehydrophilic moiety.
 71. The fluid as claimed in claim 63 wherein themember is an inorganic salt and is present in an amount of from about0.1% to about 30% by weight.
 72. The fluid as claimed in claim 63wherein the member is an organic acid or salt thereof and is present inan amount of from about 0.1% to about 10% by weight.
 73. The fluid as inclaim 63 wherein the surfactant is represented by the formula (I)

wherein R₁ represents alkyl, alkenyl, alkylarylalkylene,alkenylarylalkylene, alkylaminoalkylene, alkenylaminoalkylene,alkylamidoalkylene, or alkenylamidoalkylene, wherein each of the alkylgroups have from about 14 to about 24 carbon atoms and may be branchedor straight chained and saturated or unsaturated, and wherein thealkylene groups have from about 1 to about 6 carbon atoms, R₂ and R₃ areindependently aliphatic chains having from about 1 to about 30 carbonatoms, and R₄ is a hydrocarbyl radical with a chain length of about 1 toabout
 4. 74. The fluid of claim 73 wherein R₁ is selected from the groupconsisting of tetradecyl, hexadecyl, octadecenyl, and octadecyl.
 75. Thefluid of claim 73 wherein R₁ is an alkyl group derived from tallow,coco, soya bean, or rapeseed oil.
 76. The fluid of claim 73 wherein thealkyl and alkenyl groups of R₁ are selected from alkyl groups andalkenyl groups respectively having from about 16 to about 22 carbonatoms.
 77. The fluid of claim 73 wherein R₂ and. R₃ are independentlyalkyl, alkenyl, arylalkyl, hydroxyalkyl, carboxyalkyl, orhydroxyalkylpolyoxyalkylene, each having about 1 to about 10 carbonatoms.
 78. The fluid of claim 73 wherein R₂ and R₃ are independentlymethyl, ethyl, benzyl, hydroxyethyl, hydroxypropyl, carboxymethyl, orcarboxyethyl.
 79. The fluid of claim 73 wherein R₄ is methylene orethylene.
 80. The fluid of claim 73 wherein R₂ and R₃ are eachbeta-hydroxyethyl.
 81. The fluid of claim 80 wherein R₁ isRCONHCH₂CH₂CH₂— wherein R is an alkyl group having from about 14 toabout 24 carbon atoms which may be branched or straight chained andwhich may be saturated or unsaturated.
 82. The fluid of claim 81 whereinR₂ and R₃ are each methyl.
 83. The fluid of claim 82 wherein R₁ isRCQNHCH₂CH₂CH₂— wherein R is an alkyl group having from about 14 toabout 24 carbon atom which may be branched or straight chained and whichmay be saturated or unsaturated.
 84. The fluid of claim 63 wherein thezwitterionic surfactant is selected from the group consisting ofdihydroxyethyl glycinates and alkylamidopropyl betaines.
 85. The fluidof claim 84 wherein the zwitterionic surfactant is oleamidopropylbetaine.
 86. The fluid of claim 73 wherein the amount of zwitterionicsurfactant is from about 0.5% to about 6% by weight of the fluid. 87.The fluid of claim 73 wherein the anionic surfactant is present at 0.9%or less by weight of the fluid.
 88. The fluid of claim 84 wherein theamount of zwitterionic surfactant is from about 0.5% to about 6% byweight of the fluid.
 89. The fluid of claim 85 wherein the anionicsurfactant is present at 0.9% or less by weight of the fluid.
 90. Aviscoelastic fluid comprising: (1) an aqueous medium; (2) an amphotericsurfactant; and (3) a member selected from the group consisting oforganic acids, organic acid salts, inorganic salts, and combinations ofone or more organic acids or organic acid salts with one or moreinorganic salts; wherein the fluid exhibits the property ofviscoelasticity.
 91. The fluid as claimed in claim 90 wherein the amountof the surfactant is from about 0.5% to about 10% by weight of thefluid.
 92. The fluid as claimed in claim 90 wherein the member is aninorganic salt and is present in an amount of from about 0.1% to about30% by weight.
 93. The fluid as claimed in claim 90 wherein the memberis an organic acid or salt thereof and is present in an amount of fromabout 0.1% to about 10% by weight.
 94. The fluid of claim 90 wherein thesurfactant is represented by formula

wherein R₁ represents alkyl, alkenyl, alkylarylalkylene,alkenylarylalkylene, alkylaminoalkylene, alkenylaminoalkylene,alkylamidoalkylene, or alkenylamidoalkylene, wherein each of the alkylgroups have from about 14 to about 24 carbon atoms and may be branchedor straight chained and saturated or unsaturated, and wherein thealkylene groups have from about 1 to about 6 carbon atoms, R₂ isselected from the group of alkyl, alkenyl, arylalkyl, hydroxyalkyl,carboxyalkyl, and hydroxyalkyl polyoxyalkylene, each having from about 1to about 10 carbon atoms, and R₄ is a hydrocarbyl radical with chainlength of about 1 to about
 4. 95. The viscoelastic fluid of claim 90wherein R₁ represents alkyl having from about 16 to about 22 carbonatoms or RCONHCH₂CR₂CH₂—, wherein R is an alkyl group having from about16 to about 22 carbon atoms, wherein R₂ and R₃ are, independently,methyl, ethyl, benzyl, hydroxyethyl, hydroxypropyl, carboxymethyl, orcarboxyethyl, and wherein R₄ is methylene or ethylene.
 96. The fluid ofclaim 90 wherein the surfactant is selected from among amphotericimidazoline-derived dipropionates.
 97. The fluid of claim 90 wherein thesurfactant is disodium tallowiminodipropionate.
 98. The fluid of claim90 wherein the aqueous medium is water, the fluid comprising greaterthan or equal to about 50% water by weight.
 99. The fluid of claim 94wherein the aqueous medium is water, the fluid comprising greater thanor equal to about 50% water by weight.